Imparting color to coated paperboard



Feb. 27, 1945. v H. c. FISHER 2,370,344

IMPARTING COLOR T0 COATED PAPER BOARD Filed Sept. 29. 1941 CAL EN DER DRIER ATTORNEY.

Patented Feb. 27, 1945 IMPARTING COLOR TO COATED PAPERBOARD Harry 0. Fisher, Cincinnati, Ohio, assignor, by mesne assignments, to Consolidated Water Power & Paper Company, Wisconsin Rapids, Wis., a corporation oi Wisconsin Application September 29, 1941, Serial No. 412,831

3 Claims.

My invention relates to the provision of paper board with various colors and shades of colors, while employing a color coat of finely-divided mineral matter, which coat does not of itself impart the final color to the board.

I have discovered, particularly in the case of using freshly made paper board, that by sizing the same with a colored size of water soluble or dispersible character after the web formation step has been completed, and then promptly applying a color coat, containing the usual mineral matter and binder substance, I can obtain a color for the final board which is the composite of the color of the sizing material and the color coat, depending in shade upon the quantities used of the color coat.

In certain modern practices of color coating freshly made paper board and paper, quite thin films of relatively thick coating material may be applied by a practice akin to imprinting the color coating in an unbroken film of considerable thinness to the surface of the board or paper. The color coating may be one such as the usual clay coating, containing a starch or casein binder and otherwise merely the finely-divided clay or other mineral matter and water, which may be fift percent or less of the coating as applied.

In such modern coating practices, as in the older ones, the imparting of a decided color to the paper or board other than white is accomplished by coloring the wet mineral coating mixture its lf before it is applied and dried onto the paper surface. Indeed, it is common practice even with white coatings, to tint the white coating mixture before it is applied to the paper surface, to produce desired casts, e. g., a reddish or bluish cast of white after the coating is applied, dried and calendered onto the paper surface. Strongly colored coatings can be applied to a White paper surface or to one already colored in the conventional manner. By using a colored paper sur-, face under the colored mineral coating, chance imperfections in the latter are not so prominent as otherwise and a more uniform result is obtained. My invention has particular importance in these modern practices whereby, without precoloring the coating mixture and without precoloring the paper. fibres, I produce a clay or mineral coated sheet of paper or board with desired color, e. g., a red, yellow, green, etc., the underlying paper surface of which also has changed in color during the practicing of my invention.

However, my invention also has importance in connection with other coating practices, particularly where thin films of coating are applied.

In a companion application to the present one, Serial No. 406,074, filed August 8, 1941, which has now been replaced by a continuation application, S r. No. 501,320 filed September 4, 1943. I have described a practice of preparing a paper board or paper for the step of color coating, which is particularly related to processes of color coating of freshly made paper board in a continuous process of making, coating and calendering the same. This practice of preparing paper board for color coating consists in the application thereto prior to coating, of a surface size of a water solution of a substance which is plasticizable as well as water soluble, after which the sized surface is compacted and smoothed as by a breaker stack of calenders located immediately following the dryers of the web forming machine, in a paper board mill. My present practice is utilizable in connection with such a practice.

My practice is also usable in connection with practices using other water soluble sizes, which are applied to the surface of paper or paper board just prior to color coating, such as for example, ordinary starch size.

I have shown in the appended drawing an installation usable with my invention. In this installation, i represents the final drying rolls of a paper board machine, 2 indicates the web of paper board, 3 are the rolls of the breaker stack of calender rolls, 4 are boxes used to apply size to the board on the breaker stack by feeding the same to the rolls. After passing the breaker stack and while the sized surface is relatively moist, the board passes to the coater rolls 5, supplied with a controlled film of coating by means of applicator rolls indicated at 6, to which the coating is applied at 1. From the coater the web will pass through drying equipment and finally will be calendered, as in the usual practice.

The colored sizing material will be applied by me as an example in, the :boxes .4, or in some of the other boxes, as the case may be. The essentials of the colored size are that it be water dispersible or soluble, and preferably that it be not completely dried when the board comes to the coater. The practice is particularly applicable to freshly made board, as already discussed, For the best results, particular organic water soluble dyestuffs are used in m parctice. If the sizing material disclosed in my said companion application be used, the dyestufl may be mixed in o the size, such as for example, in a five per cent solution of olyvinyl alcohol in water or polyvinyl alcohol in water extended with starch solution. It may be incorporated along with a wetting or penetration imparting agent, to control the final gloss of an ink imprint upon the final board. If used with a usual starch size the dyestuff will be incorporated into this size. with starch size alone there will be less improvement in the final smoothness of board.

A wax size will not best serve the purposes of my invention, which relies upon the water penetrability of the size. However, the lubricating effect of wax size in a, concentrated dye solution may be necessary to reduce picking of the paper web on the calender rolls in which event inclusion of a small amount of wax size in the dye solution may be worth tolerating for that reason.

Instead of incorporating the dyestuif into the sizing solution it may be applied to the paper surface from separate solution, free of size, before, or preferably, after the sizing solution. A calender box at 4a, preceding the one at 4 carrying sizing solution, or at 4b, following 4, can be used for the dye solution. For a strong color, not obtainable with a single calender box dye solution, the sizing solution and additional calender box solutions all may be dyed. These solutions all may comprise the single desired color resulting in an increase in intensity of that color as one calender application reinforces another, or may comprise solutions of different colors which blend together to give the corresponding hue. Thus. two or three applications of blue dye solution, as at 4a. 4 and ib, will produce a blue color of paper surface increasing in intensity with the number of dye applications but by changing one of the solutions to another color, e. g., yellow, a greenishhue will result. Usually, however, such a color blend will be prepared in a single solution which may be applied to the paper surface in one or more steps as desired. The drawing illustrates the calender boxes for one side of the sheet only.

The number of calender solutions to be used, and their relative points of application are practical matters dependin upon physical properties of the paper web. A relatively thin or weak web or one running at high speed may make it impractical to use more than one calender box solution; in such case, a single solution containing both size and color must suflice. When dye solution is applied to the paper web on the calender stack before the sizing solution there is a gradual transfer of color from the web to the following size solution, depending in amount upon the extent to which the dye is fixed upon the paper fibres. If a rap d change from one color of paper to another is desired, this requiring a size solution free of color, the size solution should be applied before the dye solution to prevent an absorption of dye from paper surface into size solution.

For example, using a red dye dissolved in the size of my companion application, and using the breaker stack of calenders for an applicator, the board with moisture still predominant in the sized surface, as compared with moisture in the rest of the board, will come to the color coater. The color coating required is one which is water soluble or dispersible and may comprise the usual starch binder, finely-divided mineral matter, water, etc., with the water content controlled, say to around 50% of the dissolved and suspended matter for some coatings.

The result of the application of the wet color coating is that dye in the size or of the paper surface dissolves into the wet color coating modifying its color. With a red dye, for example, and with a thin color coat, the result, using a white clay color coat, will be the same reddish color, modified by the white of the clay. The final color is a composite of the reddish color of the clay coat and the reddish color of calender stained surface of size and paper board showing therethrough. With a plasticized, smoothed and compacted surface treatment of size, which lays the fibres in the board, a uniform and pleasing color can be obtained more easily by adding dye as a preparation for the step of clay or mineral coating than if the color were applied in the clay coating. This is particularly true in the practice described above as an example because the clay color coat is quite thin, and slight variations in thickness of the layer of coating will make a big difference in the shade of the color if the color is applied by pigment or dye in the clay color coat alone. Moreover, the expense and labor involved in preparing and using clay color coats of various colors is eliminated.

Also when using a plasticizable size which is also moisture penetrable, the final calendering of the coated web after drying will function in further spreading the entire body of material imposed on the sheet and thus further rendering uniform the color in the final product.

In the case of a plain starch surface size into which dye is incorporated, followed by a white clay coating under conditions when the moisture in the coating and the effect of that moisture on the size is such as to absorb some of the dye from the size into the body of the clay coating, the effect is comparative except that the smoothness of the final product will depend more upon the board making practice and be less assisted by the starch sizing. This is true also when a solution of dye in water free from any surface sizing substance is used.

Certain coloring materials can be used more satisfactorily than others in my process. Pigments, as a class, are inoperative, although there may be some of such ultra fineness and high dispersibility in water, of which I am unaware, that they are usable. The requirement is a dyestuff 'which actually dissolves in water or calender size solution in Water to form a solution of clarity and strength and which, after it colors the paper surface, is compatible with the subsequently applied wet clay or color coat to the extent that; its resolution in the water of the color coat leads to its dispersion throughout the solids of the color coat there to dye it a uniform color. Sensitivity of the dyestuff to acidic or basic conditions also governs the selection of dye. A color coat with alkaline reaction responds well to acid dyes whereas a basic dye will mottle strongly. Dyes of other classes will perform accordingly as they are affected by the conditions noted.

Three dyestuffs, among others, which work well in my process and which in combination produce a variety of hues are the acid dyes Eosine, Tartrazine and Erioglaucine. Eosine produces a bright pinkish red, Tartrazine a yellow and Ericglaucin'e a greenish blue. These dyes have color indices of 768, 640 and 6'71 respectively. ("Colour Index of the Society of Dyers and Colourists" by Rowe, 1st edition, June 1924.) When dissolved singly in the calender size solution or in water alone and used in the calender boxes on the breaker stack of calenders against the surface of board to be color coated thereafter, as described, their particular colors are developed. When two or more of the dyes are mixed together in solution and applied to the web, or a solution of one dye is applied to the web after a solution of an-, other, etc., followed by the color coating operation, and drying and calendering of the coated web, a color coated paper of blended hue results. For example, Tartrazine with Erioglaucine produces green, Eosine with Erioglaucine produces purple, the three together give brown, etc., according to the well known laws of color blending.

When, in a practice of color coating paper or board, a thin film of wet coating material is applied to the paper surface by a method akin to imprinting the color coating in an unbroken film, as by ccater rolls of the appended drawing, the use of a dye solution in water or size in the boxes of the breaker stack of calenders will result in a coloring of the wet coating material itself on 'coater rolls 5, as the coating machine continues to operate. Although the amount of color introduced into the coating itself through this medium is small, it does help promote a uniform color of coating.

I am not aware of any work being done in the past directed to color coating of a paper board or paper which has been prepared for color coating by the imposition of a dyed surface with adherent material in water solution, to the end of subse-- quent absorption of dye into the final color coat and thus modifying it throughout, in a uniform manner. Neither am I aware of such a procedure being used to modify the color of the color coat by using a dyed paper surface in the absence of a sized paper surface. My discovery that this does in fact take place forms the basis of my present invention which is not dependent upon the use of any dyes or pigments in particular either in the size or in the color coat.

When referring to imposing a size containing dyestuff" in the claims that follow, I intend to include applications in one or more stages with the dye itself brought into the size before application or during application by means of a distinct dye imposing stage, in either event the dyebeing in the size in preparation for the color coating step.

Modifications may be made in my invention without departing from the spirit of it. Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In a process for preparing a mineral coated paper surface of distinct hue, the steps which consist in treating the web surface being colored with water soluble dyestuff and as part of this treatment sizing it with an adherent water soluble size and then promptly applyingan aqueous vehicle mineral coating mixture which is white in color to the 'web, with the result that dye is absorbed from the stained paper surface into the wet mineral-coating, saldmineral coating being applied in a thin coat containing finely divided mineral matter, binder and a relatively small amount of water.

2. The process of claim 1 in which the web is compacted and smoothed after the sizing and prior to the deposition of the mineral coating.

3. In a process for' preparing a uniformly colored mineral coated paper web, the steps which consist in first imposing on the web a moist com-- position composed of an adherent water soluble size and water soluble dye, as the essential coloring component thereof, and then asa part of a continuous treatment and before the size is dried, mineral coating the web with an aqueous vehicle mineral pigment coating mixture wherein the mineral pigment is the essential coloring component and of contrasting color to said dye, with the result that the dye is absorbed from the size into the final mineral coating to impart its color HARRY C. FISHER.- 

